You've driven through it many times. Ever wondered what's inside it? Bob Hazen went in and tweeted these photos while waiting to do his live reports about the Squirrel Hill Tunnel weekend closure on Pittsburgh's Action News 4 This Morning.

The closure will be in effect from 10 p.m. Friday until 6 a.m. Monday. Work will include paving of the tunnel, tile placement, waterline installation, sandstone and brick cleaning, lighting and other miscellaneous construction.

The inbound (westbound) lanes of the tunnel will remain open, but short-term inbound traffic stoppages may occur for equipment access and material removal.

Drivers should expect significant delays and consider alternate routes. Different detours are being used during the day and night to minimize the effect the closure will have on nearby businesses.

If significant congestion and delays are occurring during the outbound closure, PennDOT has suggested the following alternative:

-From eastbound I-376, take the Forbes Avenue (Exit 72A) to Oakland-Continue on Forbes Avenue through Oakland-Make left onto South Bellafield Avenue-Make right onto Fifth Avenue-Continue east on Fifth Avenue-Make right onto Penn Avenue (Route 380/8)-Continue through Wilkinsburg-Access Parkway East in Forest Hills

Photos: Take a peek inside the Squirrel Hill Tunnel

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Bob Hazen

Bob Hazen went inside the Squirrel Hill Tunnel and tweeted pictures while he had some time to spare between his live reports on Pittsburgh's Action News 4 This Morning.

CONGESTED, SO BE SURE TO ALLOW FOR EXTRA TIME. THE TUNNEL WILL REOPEN BY 6:00 MONDAY MORNING. THIS WILL BE THE LAST FULL CLOSURE OF THE TUNNEL, AT LEAST FOR THIS PROJECT. I HOPE SO. WHAT WORK HAS BEEN GOING ON INSIDE THE TUNNEL? PITTSBURGH ACTION NEWS 4 REPORTER SHELDON INGRAM HAS THE ANSWER. YOU'RE LIVE OUTSIDE THE TUNNELS TONIGHT. TEH THESE TILES, WHAT'S GOING ON? Reporter: THE SQUIR BEEN SHUTTING DOWN OFF AND ON FOR TWO AND A HALF YEARS, SO SURELY EVERYONE CAN HANDLE ONE MORE FOR THIS COMING WEEKEND. WE CONSIDER ALL THE WORK GOING INTO IT, FOLKS CAN BE REASONABLE ABOUT THIS NEXT SHUTDOWN. IT TOOK TWO AND A HALF YEARS TO GET THE SQUIRREL HILL TUNNEL INTO DECENT SHAPE. INSIDE THAT TIME FRAME, 26 CONTRACTORS TEAMED UP FOR THE WORK, REPLACING THE TILES IS SO METICULOUS, THE PIECES HAVE TO BE REPLACED BY HAND, ONE AT A TIME. PENNDOT HAD TO BRING THEM IN FROM EUROPE. WORKERS FINISHED THAT JOB THIS WEEKEND. HERE'S A LOOK AT SOME OF THE OTHER PROJECT WORK. CONTRACTORS USE GERMAN-MADE TILES BECAUSE NO DOMESTIC MANUFACTURERS MET SPECIFICATIONS. WORKERS INSTALLED THE STATE OF THE ART LIGHTING SYSTEM THAT AUTOMATICALLY ADJUSTS TO OUTDOOR LIGHT AS DRIVERS ENTER THE TUNNEL. REPAVING THE SURFACE HAPPENS THIS WEEKEND, AND THEY HAD TO REPLACE THE TILES, HAND BY HAND. WANT TO GUESS HOW MANY? 50,000. Reporter: HIGHER. 75,000? HIGHER. 85,000? 100,000? Reporter: TRY HIGHER. WOW, THAT'S A LOT OF TILES. Reporter: YOU'RE STILL OFF. TRY 350,000 PIECES OF TILE. THAT AMOUNTS TO 40,000 SQUARE FEET, OR 22 MILES OF HAND-PLACED TILES. NOW YOU THINK THE DRIVERS WILL BE HAPPY WHEN THE TUNNEL IS DONE, TRY THE WORKERS WHO HAVE TO DO THE RETILING WORK.